The art of fabric filtration has been practiced for a number of years in the removal of particulates from gas streams. The basic principal employed is that particulates in a gas stream are prevented from passing through a fabric having sufficiently smaller air passages than the particles desired to be trapped. Flow of the gas stream through the fabric is such that the mechanisms of impaction, interception and diffusion cause the particles to become entrapped. Initially, particles are captured on and within the fabric. Eventually, particles are captured by a built up "cake" of particulates which covers the fabric.
There are a variety of methods employed to direct and filter a gas stream to entrap particulates. These methods also include a means of periodic cleaning with pressurized gas to extend the useable life of fabric filter media Typically, filter media must be replaced as it becomes blinded or perforated.
Generally, contaminated gas enters a dirty gas plenum, passes through the filtration fabric and exits through a clean gas plenum. The method of mounting and replacing filter media varies according to specific manufacturers' designs.
Some designs use a rigid self supporting fabric. The rigid fabric is formed into a desired shape and mounted in frames. These rigid fabric filters are commercially known as "cartridges." Cartridges have the ability to collect the particulates on either side of the fabric, depending on the design employed.
Other designs use fabric that has been shaped into tubes or envelopes in the form of filter bags, also commercially known as simply "bags." The bags are attached to orifices in a tube sheet. The purpose of the tube sheet is to direct the gas flow to the inside of the filter bag, thus forcing gas to pass through fabric of the filter bag before it can exit through the clean air plenum. Units designed in this manner collect particulates on the inside of the bag and generally require periodic shaking to dislodge the particulates. Dislodged particles are allowed to drop to a collection area below a tube sheet. Reverse air flow through the fabric bags can also be used to assist in dislodging particulates. Optionally, reverse air flow through the bags functions as the primary means of particulate removal.
Other designs also use a fabric which has been formed into filter bags. The filter bags are suspended from an orifice into a dirty gas plenum where gas is forced to pass through the fabric of the suspended bags to enter the center of the bag and to exit through the orifice into a clean gas plenum. Periodic cleaning of the fabric is accomplished by sending a pressure jet of air through the suspended bags in a reverse flow direction. This type of design requires a rigid cage structure to prevent collapse of the filter bag.
All of these devices require that periodic servicing be conducted. Servicing involves replacement of used media, thus exposing personnel to particulate matter. Although some designs have attempted to minimize this exposure, particularly cartridge type designs, there are no designs which eliminate personnel exposure to particulates. Some tube type units are designed to allow removal of a complete bank of tubes to a service area where they are manually serviced. In designs where the fabric bags are suspended, attempts have been made to service the bags entirely from the clean air plenum. However, due to small amounts of very fine material passing through the fabric into the clean air plenum, the clean air plenum is not entirely free of particulates.
Another problem with bags is fabric ruptures. When fabric ruptures occur, the downstream gas becomes contaminated with particulates. Tracer particles sensitive to ultraviolet light are sent through the baghouse to locate the rupture. Once the rupture is located, which can be difficult, the fabric is replaced.
It is an object of this invention to provide a particulate free environment for personnel replacing baghouse filter bags.
It is another object of this invention to provide a baghouse which permits replacement of filter bags while operating the baghouse to improve on-stream availability.
It is another object of this invention to provide a baghouse design which facilitates replacement of filter bags.
It is another object of this invention to provide a clean method and apparatus for disposing of used filter bags.
It is another object of this invention to increase baghouse cleaning efficiency and the amount of particulates removed.
It is another object of this invention to limit downstream contamination due to fabric rupture.
It is another object of this invention to simplify detection of fabric ruptures.